Michael Jackson did not sing in the episode of The Simpsons in which he appeared as a mental patient, according to Lisa Simpson herself.

Actress Yeardley Smith, the voice of the most intelligent member of the Simpson family, has revealed to TMZ.com that, due to contractual reasons, Jackson‘s record label Sony blocked him from singing the song ‘Happy Birthday Lisa’, which he had written especially for the episode ‘Stark Raving Dad’, first aired in September 1991.

Instead, he handpicked a Michael Jackson impersonator called Kipp Lennon – who also provided Jackson’s singing voice in the US miniseries The Jacksons: An American Dream – to sing just like him, even on snippets of ‘Billie Jean’ and ‘Ben’.

In the One Flew Over The Cuckoo’s Nest-inspired episode, Jackson – credited as John Jay Smith – plays mental patient Leon Kompowsky, a large white man who pretends to be and acts like the King Of Pop. Homer Simpson meets him after being institutionalised when he is accused of being a “free thinking anarchist” by Mr Burns for turning up to work in a pink shirt.

You can hear the song Jackson supposedly sung in The Simpsons by scrolling down and clicking the video below.